1. Field of the Invention
The present invention generally relates to a transmission device and, more particularly, to a transmission device including an automatic transmission that performs a shift change by a switching operation of a twin clutch.
2. Description of Related Art
Conventionally, there has been known an automatic transmission that includes a hydraulic twin clutch for a transmission and that can perform a shift change without interrupting the transmission of a rotational drive force by changing over, with a neighboring gear, a connection state from a clutch on one side to a clutch on the other side.
JP-A-2007-92907 discloses a twin clutch type automatic transmission that includes an orifice mechanism by which lowering of an oil pressure in a clutch on a side where the clutch is disconnected by a swapping operation is alleviated, thus suppressing a shift shock, which is caused due to an excessively high lowering speed of the oil pressure.
With respect to a twin clutch type automatic transmission, there has been known the constitution where a transmission control is performed by a twin clutch and a half clutch control at the time of starting is performed by a centrifugal clutch provided independently from the twin clutch. In studying the miniaturization of such an automatic transmission, as one of methods for miniaturizing the automatic transmission, it is considered that the centrifugal clutch is removed by also performing the half clutch control at the time of starting using the twin clutch.
However, when the centrifugal clutch is simply removed from the twin clutch type transmission disclosed in JP-A-2007-92907, a lowering speed of an oil pressure at the time of disconnecting the clutch is suppressed by the orifice mechanism. Hence, for example, at the time of rapid deceleration that may cause locking of a drive wheel immediately after a shift change, when an oil temperature of a working oil is low and has high viscosity, it takes time before a working oil pressure in the clutch on a disconnection side is completely lowered. Therefor, an engine rotational speed is lowered before the clutch is brought into a disconnection state whereby there is a possibility that an engine stall occurs. Accordingly, it is necessary to take a countermeasure against such an engine stall.